1. Field of the Invention
The invention relates to a semiconductor optical integrated circuit device and a method for fabricating the same by utilizing a metal organic vapor phase epitaxy with a waveguide direction band gap energy control technique.
2. Description of the Related Art
The value and importance of developments in fabrication processes of monolithic integration optical devices for multiple channel optical communication systems and high speed optical processing are increasing. It is required to develop useful and simple fabrication processes of the optical monolithic integration devices to secure a high yield and a uniformity in device performances. The monolithic optical integration device generally comprises active and passive regions, both of which have different band gap energies or different wavelength compositions from each other. For that reason, the fabrication processes are necessarily subject to a complication and a difficulty to secure the uniformity in the device performance as well as an inferiority in accuracy in alignment of each element and in device size.
One of the prior art fabrication processes of a single wavelength tunable distributed Bragg reflector laser device is disclosed in Japanese laid-open patent application No. 4-150383. As illustrated in FIGS. 1A to 1C, a multiple quantum well layer 5 is grown by a metal organic vapor phase epitaxy with use of paired dielectric stripe masks 20, each of which has different widths between an active region 31 and a phase control region 32 and a distributed Bragg reflector region 33. The width in the active region 31 is larger than that in the other regions 32 and 33. The multiple quantum well layer 5 and a cladding layer 6 are selectively grown on selective growth areas sandwiched between the paired dielectric stripe masks 20 respectively.
The thicknesses and the photoluminescence peak wavelengths of the epitaxial layers 4, 5, 6 and 7 grown on the selective growth area are proportional to the width of the dielectric stripe mask 20. The band gap energies of the epitaxtial layers are inversely proportional to the mask width. For that reason, the epitaxial layers having the different band gap energies, different wavelength compositions and different thicknesses are grown by a single growth process. Such simplicity in the fabrication process is able to provide a high yield and a uniformity in the device performances.
The above prior art, however, neither discloses nor suggests any useful fabrication processes for monolithic optical integration devices, although that provides the useful fabrication process for a single element involved in the optical integrated circuits.
Another prior art being directed to fabrication processes for a single wavelength tunable distributed Bragg reflector laser device is disclosed in Japanese laid-open patent application No. 4-303982 (application No. 3-67498). In this prior art, the dielectric stripe masks whose width is varied are used for the selective growth with the metal organic vapor phase epitaxy. This prior art also neither discloses nor suggests any useful fabrication processes for monolithic optical integration devices, although that provides the useful fabrication process for a single element involved in the optical integrated circuits.
The selective metal organic vapor phase epitaxy utilizing the wave guide direction band gap energy control technique by dielectric stripe masks with a varied width is reported in T. Sasaki et al. Optical Fiber Communication Conference, 1992, pp. 281-282. This prior art also neither discloses nor suggests any useful fabrication processes for monolithic optical integration devices.
One example of the fabrication processes for monolithic integrations with lasers and modulators is disclosed in M. Aoki at al. Electronics Letters, 1991, vol. 27, pp. 2138-2140. In this prior art, the fabrication processes for the optical integration device includes mesa etching process as illustrated in FIGS. 2A to 2C. The mesa etching process and any etching process provide the complication in the fabrication process of the device and cause any variation in the layer size thereby resulting in a difficulty to secure a uniformity of the device performance and in a reduction of a yield of the device.
Another prior arts directed to the fabrication process for a semiconductor optical amplifier with a window region are disclosed in I. Cha et al., 100C' 89, Kobe, paper 20 C2-2 and in Japanese Laid-open patent application No. 5-37092. The above references neither discloses not suggests useful and simple fabrication process for epitaxial layer having a variation in the band gap energy.
Another prior art directed to the fabrication processes for 4-channel optical integration device as illustrated in FIGS. 4 and 5 is disclosed in M. Yamaguchi et al. 1990, Technical Digest, 12th IEEE International Semiconductor Conference pp. 160-161. The device comprises an active region 31, a phase control region 32, a distributed Bragg reflector region 33, a modulator region and a passive waveguide region 35. The fabrication processes have the complication thereby the monolithic integration device has butt-joint structure which provides a difficulty to secure a high coupling efficiency between each elements. For that reason, it is difficult to secure a high coupling efficiency between each elements thereby resulting in a large injection current and in inferiority of the device performances.
Another prior art directed to the fabrication processes for 20-channel optical integration device including distributed is disclosed in C. E. Zah at al. Electronics Letters, December 1992, vol. 28, No. 25, pp. 2361-2362. The emission light wavelengths are different in 20-channels, as illustrated in FIGS. 6 and 7. The fabrication processes include electron beam exposure for forming gratings of the 20-channels having different grating periods. The formation processes of the different pitch gratings provides a complication in the processes and a difficulty to secure a precise grating pitch thereby resulting in a reduction of device yield and a great manufacturing cost.
Another prior art directed to the fabrication processes for optical amplifier gate switch arrays for multiple channel optical communication systems is disclosed in M. Janson at al. Electronics Letters, vol. 28, 1992, pp. 776-778. The structure of the 2.times.2 gate arrays is illustrated in FIGS. 8 and 9. The passive and active wave guides are not smoothly coupled, namely the coupling portions between the active and passive wave guide layers have discontinuities which is provides a reduction of coupling efficiency thereof. The low coupling efficiency requires a large injection current which is undesirable.
In any event, there has been no prior art for useful and simple fabrication methods for semiconductor optical integration devices including epitaxial layers in which each layer has different band gap energies along the wave guide direction, although many fabrication methods have been developed.